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1.a- She is sorry for not telling me this before.

1.b- She is sorry for not having told me this before.

2.a- She was sorry for not telling me this before.

2.b- She was sorry for not having told me this before.

I know that 1.a and 2.a are natural. (or am I wrong?) But when do we use 1.b instead of 1.a? Are 1.b and 2.b natural too? Are there any differences? When do we use 2.b instead of 2.a?

OR IF YOU LIKE YOU CAN ANSWER JUST THIS.

1. ARE THEY ALL CORRECT?

2.IF SO, WHEN WOULD YOU USE "PERFECT PARTICIPLE" INSTEAD OF "PRESENT PARTICIPLE"?
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They are all correct.
I wouldn't use the perfect versions at all, especially not in everyday conversation.
The perfect versions strike me as literary, possibly journalistic. Some speakers do sprinkle their conversations with this sort of thing though, (perhaps to appear well educated?), so it's not impossible that you might hear it.

CJ
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thank you, Jim.
I'm curious. With the specified time stated--"before," why wouldn't a past perfect be correct?

She is sorry she had not told me this BEFORE. She is sorry now for a past action.

Ikia
Past perfect is for something before the past, not just before the present.
The past is before the present. The past perfect is before the past.

She is sorry she did not tell me before. (before now)
She was sorry she had not told me before. (before then)

This is really a separate question from that which introduces the thread, of course.

CJ
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